1. Field of the Invention
The present invention relates to a proportional-integral-derivative controller (PID controller). More particularly, the present invention is related to a configuration method, program and system for determining coefficients for a PID controller.
2. Description of Related Art
Recently, robust control that uses H∞ or LMI (Linear Matrix Inequality) has been developed. Suitable design utilizing robust control is possible if reliable prior knowledge about an error limit with respect to the uncertainty of a plant is available. In many cases, however, only little plant information can be obtained or the plant information can be unreliable. In such cases, application of robust control is limited.
Proportional-integral-derivative controllers (PID controllers), which can be said to be classical, are still used for on-site designing. In some cases, a PID controller, which does not require a plant model, is used. In this case, the challenge is to determine the coefficients for the PID controller. A problem associated with a conventional way of determining PID coefficients is that, though it is theoretically effective up to a second order plant, a number of adjustments are required for a high-order plant and an unstable system.
At the time of designing a control system, a model based development (MBD) framework is effective, where SysML is used to describe how controller parameters are linked to requirements in order to derive a control strategy in a predetermined system. On the other hand, in cases where the structure of a plant is unknown, it is possible to tentatively operate the plant to a certain degree of performance and then predict the requirements for SysML. When the start is uncertain, automatic design of PID gain can be used to identify the extent of a control input influenced by an error, integral, and/or derivative. If successful, it becomes possible to start the description into a requirement diagram or a block definition diagram in SysML, and expand further from the result thereof.
Therefore, there is an increasing demand for a technique of automatically calculating a PID controller in an appropriate time setting.
It is known that there is a provision of an epoch-making method which realizes easiness of setting, where the method can be applied to a multiple-input multiple-output system by applying the concept of unfalsified control to offline control system design. Such method makes it possible to determine an optimum value of control gain by calculation. The disclosed method includes the steps of acquiring at least one input/output response data at the time of adding a step input or the like to a control target (plant) P, generating a predetermined number of or more virtual input/output response data on the basis of the data, substituting each of them into an unfalsified arithmetic expression to specify a predetermined number of or more unfalsified regions in a parameter space, and determining an optimum value of control gain in a region of a product set of a predetermined number of or more unfalsified areas by calculation by deriving a linear constraint expression from the unfalsified arithmetic expression.
It is known that there is a unfalsified control theorem that provides consistency with target performance and past experimental data without prior knowledge about a presented plant model. However, it is difficult to determine coefficients constituting a robust PID controller in an appropriate time only by a use of an unfalsified control technique.